1. Field of the Invention
The invention pertains to the field of ship""s steering systems and more particularly to reducing the wiring between steering control units of such systems and the steering mechanisms.
2. Description of the Prior Art
Ship maneuvering and course control have advanced over the years from the tiller control of the rudder to present day autopilots. Traditionally a bridge has been the command center of the ship and control functions have been performed at this location. Large ships of the present day, however, may have command stations remote from the bridge which provide better visibility for certain maneuvering situations such as harbor navigation and ship docking. Should visibility from the bridge be impaired, the control of the ship may be passed to the remote station best located for the necessary maneuvers. These remote stations are hard wired to the steering system and switching is performed with multiple deck switches and numerous electromechanical relays.
A typical steering system includes two remote command centers, an autopilot, helm, and tiller steering modes, and a mode selector switch. These systems are custom built, complex, wiring intensive, and expensive to design and build. Steering systems are a very low volume product and each customer has unique requirements and constraints. Because of the unique requirements and constraints, building complete units in advance to provide an inventory is not cost effective. Such an approach invites multiple handling of the same equipment to satisfy the customer requirements, thus increasing the cost of manufacture. Prior art designs rely on labor intensive discrete wire connections and custom wiring diagrams to satisfy customer requirements. Such an approach provides a system, which in addition to being expensive to design and build, lacks modification flexibility.
In accordance with the present invention a steering system for a ship includes a bus architecture which reduces the complexity of the system component interconnections and provides for incorporating new components and additional steering command centers. The system includes a helm wheel for follow-up steering control, a non follow-up steering control unit (NFU), and three types of devices that may be attached to the bus: Autopilot Display Units (ADU), Autopilot Interface Units (AIU), and Bus Interface Units (BIU). An ADU displays the autopilot settings and other pertinent data in addition to containing the autopilot control functions. An AIU contains elements for bus initialization, station management, follow-up control, and the autopilot, while a BIU contains software which can be configured to perform a selected function. All three, ADU, AIU, and BIU contain the necessary software and hardware for coupling to the bus. Cable (bus) interface units (CIU) at each station allow for the coupling of a multiplicity of units (ADU, BIU) to the bus at the respective stations. Because the closed loop controller function is contained entirely within the AIU, bus latency is not a critical parameter. Only control parameters, which are not sensitive to latency effects of the bus, are sent from the ADU to the AIU. The helm wheel is not coupled to the bus but is directly coupled to a follow-up function in the AIU. The helm wheel may be selected for follow-up control and in the event of a bus failure may be selected to provide basic closed loop rudder control. The NFU is a mechanical lever which controls a voltage source that is coupled through a switch to directly apply control voltages to the solenoid activating rudder movement without any processor or bus intervention. The switch is positioned to select between autopilot control and NFU control. Since the NFU is located outside all of the bus and interface units, it acts as a complete backup to any catastrophic system failure.
A multiplicity of AIUs are provide. Should an AIU fail, the AIU functions are switched to another AIU and the system operation continues without further interruption.
On ships having more than one rudder, at least one AIU is employed for each rudder. The AIUs, respectively associated with the rudders are employed in a master/slave relationship, the master being determined through arbitration of proprietary system messages. When the system is in the automatic control mode, heading order signals are received by the master which then computes the rudder order and relays this information to the slave units. When the system is in a non-automatic control mode, each AIU receives its own helm order, whether from the helm on the bridge or from elements at remote locations from which it determines the rudder order for its associated rudder. Should the master fail, a new mastership is established by a re-arbitration among the remaining AIUs using the proprietary system messages.
The invention will now be described in greater detail with reference to the accompanying drawings.